Currently, active matrix organic light emitting device (“AMOLED”) displays are being introduced. The advantages of such displays include lower power consumption, manufacturing flexibility and faster refresh rate over conventional liquid crystal displays. In contrast to conventional liquid crystal displays, there is no backlighting in an AMOLED display as each pixel consists of different colored OLEDs emitting light independently. The OLEDs emit light based on current supplied through a drive transistor. The power consumed in each pixel has a direct relation with the magnitude of the generated light in that pixel. As a result, the uneven power consumption profile, the anisotropic lateral heat conduction of the panel (e.g. lower conduction in the panel edges), and the differential heat convection in vertical orientation lead to a highly non-uniform surface temperature profile.
The non-uniformity of the temperature severely impacts the quality of the display by adding visual spatio-temporal artifacts. That is due to the strong thermo-electrical-optical coupling in the characteristics of the pixel circuits, such as the thermal dependency of the voltage-current characteristic of the thin film transistors (TFTs) that are used as drive transistors and their short-time threshold voltage aging rate. The drive-in current of the TFT determines the pixel's OLED luminance. Since the pixel circuits are voltage programmable, the spatial-temporal thermal profile of the display surface changing the voltage-current characteristic of the drive transistor impacts the quality of the display. The rate of the short-time aging of the thin film transistor devices is also temperature dependent. If the temperature of each pixel is known, proper corrections can be applied to the video stream in order to compensate for the unwanted thermal-driven visual effects.
However, determining the temperature of each pixel presents difficulties in the need for additional components such as thermal sensors and/or additional computational circuitry to analyze the performance of each pixel during the use of the display. Accurate yet efficient real-time extraction of surface thermal profiles is therefore needed. Such information is critical to provide proper compensation for the thermal effects in large area AMOLED displays.